A series of new analogs of enkephalin have been developed. These consist of dimers, crosslinked at the carboxy terminal by diaminoalkanes. A new method of synthesis has been developed. The dimeric pentapeptide enkephalins have been purified, and their structure and molecular weight have been confirmed by several physical chemical techniques. These new analogs have been assayed for activity in a variety of radioligand assays employing whole brain membrane and neuroblastoma-glioma cells. The new analogs show extremely high potency for the "delta" opiate receptor and possess the best "delta" specificity ever reported. These compounds are useful in the characterization of the opiate receptor in the membrane, and should be valuable for a wide variety of autoradiographic and pharmacological applications.